It was noted that, due to the constraint of electro-neutrality, O-ion vacancies could be generated in this materials by the replacement of tetravalent Ti ions with divalent metal ions. By increasing the intrinsic O-vacancy concentration in this way, an increase in available hopping sites was produced. The increase in vacant sites facilitated O transport through the crystal, and thereby increased the possibility of oxide-ion conductivity. The synthesis of samples was carried out by using standard solid-state techniques, using Ca and Mg as dopants. The site solubility limits for both species were deduced from powder X-ray diffraction data. The conductivity behaviour of phase pure compounds was investigated by using alternating-current impedance spectroscopy and 4-point direct-current measurements, for a range of O partial pressures. The B-site solubility limit for Mg was found to be between 5 and 7%. A sample of SrTi0.95Mg0.05O2.95 exhibited an increased conductivity, and reduced activation energy for conduction, as compared with undoped SrTiO3. Direct-current measurements of the same material confirmed that an increased p-type behaviour of the system was associated with Mg doping at high O partial pressures.

B-Site Doped Strontium Titanate as a Potential SOFC Substrate. T.D.McColm, J.T.S.Irvine: Ionics, 2001, 7[1-2], 116-21